which means that the super calls the instance method B#m on a receiver that is not an instance of B. It's not what makes the super call to pick the main object as a receiver in this case. I would expect it to use the "self" object that the block captures, i.e. the class object C, and thus an exception "no superclass method `m' (NoMethodError)" should be raised.

class B
def m
p self
puts self.class.to_s + '::m'
end
end

class C < B
q = Proc.new do
p self
super()
end

mq = define_method :m, &q

mq.call
end

BTW: The behavior is even worse in Ruby 1.9:
ruby 1.9.1p129 (2009-05-12 revision 23412) [i386-mswin32]
C
a.rb:11:in ==': wrong number of arguments(0 for 1) (ArgumentError)
from a.rb:11:inblock in class:C'
from a.rb:16:in call'
from a.rb:16:inclass:C'
from a.rb:8:in `'
=end